1) Flexibility. Currently, it supports NMEA, uBlox, SiRF, MediaTek (DIYDrones Custom), ArduIMU Binary, ArduPilot ASCII, ArduPilot Mega Binary and UavDevBoard.
2) Flexible screen size. My original intent was to use this program on a Netbook at 1280X600 but it will go as small as 800X400.
3) Ease of use. There are LOTS of other GCS applications out there that show far more data. The issue I've had is getting them to work.